Vietnam is a 30-year nightmare, from which Jim Doyle is still trying to wake.

Jim was just 18 when he went to war, and returned a changed man

Every week he sees a psychiatrist, but no-one can free him from the demons of war.

The smallest things - like the smell of diesel - bring the memories flooding back.

But it is the big things that worry him most.

"Nobody who has ever been to war wants to see anybody else go there," he said.

"So Iraq has been a very difficult time.

"War is hell," he adds. "It has an impact on the people who take part that never heals."

'I felt alive'

Jim was 18 when he went into battle - just a year out of high school.

When I got back it was like I was invisible. People averted their eyes - I just wanted them to say something, anything

Jim Doyle

But he was quickly on the front line, engaging the enemy in an area known as the Iron Triangle.

"We'd ambush them, we would be ambushed. You never knew from one day to the next whether you would live or die.

"All I wanted to do was get out of there, but I had never felt so alive."

He survived a year, despite being injured by a bomb. But it was back home where his problems really began.

Many Americans, disillusioned with the war, turned their scorn on the soldiers who returned. It is a fact that still leaves many bitter to this day.

VETERANS ON THE STREETS

One in four homeless are veterans

Some 300,000 veterans are homeless on any night

About 47% of them are from the Vietnam era

Source: US Dept. Veteran Affairs

Psychologists say it was also the root of many problems. Veterans suppressed their emotions, turning to drink and drugs to cope, while some ended up on the streets.

Today, 300,000 war veterans are homeless across America on any one night. Half of them fought in Vietnam.

"When I got back it was like I was invisible," said Jim. "People averted their eyes - I just wanted them to say something, anything."

"But I had some serious adjustments to make, especially at home. I was abusing drugs and alcohol for years afterwards.

"I am finally beginning to realise that the war took the last of my childhood, and I was not able to move on."

'Act of betrayal'

Intelligence officer David Curry was based in a bar, not the jungle during his Vietnam war.

David Curry turned against the war during his time as an intelligence officer

But he did not escape the psychological scars.

Mr Curry spied on US soldiers who did not support the war effort. Sometimes he interrogated them.

"I remember gradually getting more and more disillusioned with the job," he told the BBC.

"I helped to identify three South Vietnamese soldiers working against us and I later found out that those people were killed. That was when I turned the corner."

He asked for a discharge, but was refused.

"Many people saw it as an act of betrayal," he said.

"But as those people moved away from me, more people came towards me - people who shared similar views.

"At first I actually thought that I hated the Vietnamese - but I saw they were people whose whole lives were being changed by forces beyond their control, and I had a whole different attitude towards my country.

"They are thoughts that still stay with me today - I get very emotional."

Jailed over drugs

Mr Curry, 56, is now a professor at the University of Missouri. But he still looks back on a life shaped by his time in Vietnam.

Vietnam still stirs strong emotions for Curry, now a university professor

He became heavily involved in the anti-war and civil rights movements - and still campaigns for peace today.

In 1983 he was jailed - and later pardoned - for supplying Vietnam veterans with cocaine when he worked as a counsellor for returning soldiers.

During that time he was diagnosed with depression and later found he had an anxiety disorder too.

"There wasn't anybody of our generation unaffected by the war," he says. "I don't think we ever should have been there."

Like Jim Doyle, and so many others, he looks back on an adolescence that never ran its course.

"There were lots of things I didn't understand," he says.

"I was excited when I got the call-up, because it meant I was finally going abroad.